The emergence and reemergence of epidemic arthropod-borne diseases has led to significant world-wide morbidity and mortality. These vector-borne viruses have not only developed highly effective strategies to hijack cellular machinery and to subvert host immune responses, but they have evolved broad host ranges, spanning insects and mammals. Whereas infection of the insect host is generally non-lethal and not associated with disease, infection of mammals can be highly pathogenic, suggesting that the viruses must use different strategies to move through each host. Little is known about the pathways required for the replication cycles of these viruses in either of their hosts, and less is understood about the innate immune pathways that restrict pathogenesis. To elucidate the cellular requirements of viral infection, we propose to employ a cell-based high-throughput RNA interference screening assay using viral infection of Drosophila cells with Rift Valley Fever virus. The powerful tools available in the Drosophila model system, including forward genetics and functional genomics, can identify cellular factors and pathways that regulate pathogenesis in a variety of contexts. Observations made in flies can then be compared to the requirements in human and mosquito cells using RNA interference methodology, thereby facilitating the identification of cellular factors either broadly utilized in the host during infection or those specific to the insect vector. To understand the differences between hosts, our system uniquely situates us to identify novel insights into survival strategies adopted by the pathogens and the host. PUBLIC HEALTH RELEVANCE: With the ever-increasing ease of global travel, insect-borne viruses endemic to different geographical regions are now becoming a serious health threat to the American population, as the spread of West Nile has illustrated. Viral pathogens that were once restricted to specific geographic regions are now able to establish persistent infections in previously unexposed populated areas. In addition, changes in global climate zones are creating optimal conditions to establish endemic areas. It is therefore crucial to understand the viral pathogenesis of newly emerging infectious diseases, in order to provide the necessary treatments for unforeseen outbreaks.